1. Field of the Invention
The present invention relates to methods for treating zeolite ores such as clinoptilolite ore for the purpose of removing discoloring impurities and brightening the zeolite and thus rendering it valuable for use in industries such as the paper industry and the coatings industry in the production of high quality products and more particularly refers to methods of converting zeolites into high quality, high brightness pigments, extenders or fillers comparable to high quality, commercial kaolin clay pigments and fillers but, in loose or packed bulk form, are only about half as dense as kaolin clay pigment.
2. Prior Art
Natural zeolites are a group of at least 34 minerals which chemically, are crystalline, hydrated aluminosilicates of alkali and alkaline earth elements usually sodium, potassium, magnesium, calcium, strontium, and barium. Structurally, the minerals are framework aluminosilicates consisting of infinitely extending three dimensional networks of AlO.sub.4 and SiO.sub.4 tetrahedra linked to each other by the sharing of all oxygens. Zeolite minerals are three-dimensional framework aluminosilicates of alkali and alkaline earth cations predominately sodium and calcium which contain highly variable amounts of water within the voids in the frameworks. The zeolite materials have open structures containing cavities filled by water molecules which are interconnected by pores or channels. When zeolite minerals are activated by heating to temperatures of over 100.degree. C., the crystal structure remains intact and the cations become coordinated with the oxygen along the inner surfaces of the cavities. Upon activation, a zeolite crystal becomes a porous solid consisting of up to 50 percent void space permeated by cavities which are interconnected by channels having diameters ranging from 2 to 7 Angstroms. The result is a natural analog of a synthetic molecular sieve which, depending on the channel size, can absorb gases and effectively separate mixtures of gases.
Deposits of zeolites are believed to have been formed from volcanic ash or lava flows coming into contact with marine waters, fresh water lakes, ground waters or saline shallow lakes. The alkalinity of the water and the type and concentration of ions it contained determine the species of the zeolite formed. Zeolite deposits may occur wherever volcanic activity has taken place near saline or alkaline water and where a sufficient amount of time has passed to effect the evolution of the minerals. There are a number of sizable zeolite deposits in Europe, the Far East, Australia, South America, and Africa. Of the more than 40 natural zeolite minerals recognized, only six are reported to occur in sufficient tonnage and purity (80% to 90% pure) to be of serious commercial interest. The six major zeolites are chabazite, mordenite, clinoptilolite, erionite, phillipsite, and analcime. Typical natural zeolites also include ferrierite, heulandite and laumontite.
Natural zeolites are mined, processed and used for their ion exchange capacity in purifying acid gases, e.g., methane or natural gas that contains hydrogen sulfide; decontaminating radioactive waste streams to recover radioactive materials, such as Cs 137 from nuclear reactor effluents; or treatment of agricultural wastes and runoff and sewage. Processing of natural zeolites prior to use includes pulverizing, classifying and calcining to drive water out of the pores.
The natural zeolites are also useful as starting materials for the preparation of synthetic zeolites. U.S. Pat. Nos. 4,401,633 and 4,401,634 describe methods for making synthetic zeolite A by heating heulandite or clinoptilolite in aqueous sodium hydroxide, filtering and reacting the filtrate with sodium aluminate to precipitate zeolite A. A similar process is disclosed in a Russian article by A. Yu. Kruppenikova, et al., titled Phase Transitions in the Recrystallization of Clinoptilolite, published by P. G. Melikishodi Institute of Physical and Organic Chemistry of the Academy of Sciences of the Georgian S. S. R. The preparation of synthetic zeolite A by hydrothermal treatment of clinoptilolite in a slurry of sodium aluminate and aqueous sodium hydroxide is disclosed in U.S. Pat. No. 4,247,524.
Attempts to upgrade the zeolite content in predominantly chabazite ores by size classification using wet cycloning and the shaking table are described in a paper entitled Beneficiation of Natural Zeolites From Bowie, Ariz.: A Preliminary Report by K. D. Mondale, F. A. Mumpton and F. F. Aplan, pp. 527-537, Zeolite '76, published by State University College, Brockport, N.Y., in 1976.
U.S. Pat. No. 3,189,557 describes a process for removing calcite fines from a montmorillonite ore by dry milling, screening to remove calcite fines, forming an aqueous slurry, centrifuging the slurry to remove calcite fines, adding a humectant and drum drying the resulting humectant-containing slurry. There results a rapidly rehydratable material useful as a beer stabilizer and purifier or as an additive to laundry starch.
U.S. Pat. Nos. 2,173,909 and 3,902,993 disclose the use of air flotation for treating zeolitic ores to separate zeolite from the amorphous gangue present in said ores.
Synthetic zeolites have been used as catalyst carriers and water softeners. Numerous patent and other prior art publications are concerned with processes for regenerating or recovering the zeolitic particles from spent catalyst or water softener. Included are U.S. Pat. No. 1,570,854, Japanese Pat. No. 5369 (1954) and East German Pat. No. 85072 (1971).
It has been reported that finely ground clinoptilolite classified by wet or dry cycloning into a -0 .mu.m product having a brightness of 80 has been produced in Japan (Takasaka in Funsai, 1975, 20 pp. 127-134, 142). Pulverized zeolite ore (60% of 2 to 10 or 20 .mu.m) reportedly has been used in Japan to manufacture paper (Kokai 73,099,402; Kokai 70,041,044). Kobor et al reported in Papiripar, 1968, 12(2), 44-50 (Hung.) that Hungarian zeolite is not suited for the manufacture of wood-free paper, that the zeolite shows medium whiteness and a high degree of dispersion and that paper manufactured with zeolite as filler instead of kaolin shows increased bulk and decreased elasticity. The low brightness level of these materials render them unsuitable for use in the production of paper of the quality demanded in the United States and other parts of the world.